Influence of ceramic crown design (translucent monolithic zirconia vs. bilayered) of implant-supported single crowns after mechanical cycling.

OBJECTIVES: This study aimed to assess the influence of translucent monolithic versus bilayered crowns and whether the use of a CoCr base abutments affects the fatigue and fracture resistance of screwed implant-supported single crowns with external connections under mechanical cycling. MATERIALS AND METHODS: Fifty specimens were divided into groups: (1) metal-ceramic (MC) crown, (2) veneered zirconia crown (Zr), (3) veneered zirconia crown with a CoCr base abutment (ZrB), (4) monolithic translucent zirconia crown (MZr), and (5) monolithic translucent zirconia crown with a CoCr base abutment (MZrB). Specimens underwent mechanical cycling (5 × 106 cycles; 150 N) evaluating fatigue resistance (number of failures) and those that failed were subsequently subjected to fractographic analyses (stereomicroscope and scanning electron microscope) to evaluate failure location and area, and maximum fracture load was also measured. RESULTS: The failure-related survival rate (100%) and maximum fracture resistance of the MZrB were significantly higher than those of MC and Zr (50%; p < 0.05). There were no significant differences in the failure rate and fracture resistance when a CoCr base abutment was used or not in the translucent monolithic Zr groups (p > 0.05;MZrB vs. MZr). Failure location, with MC crowns' fractures, noted at the screw area (p = 0.043), while all-ceramic crowns were mostly in the cuspid and to failure area, the Zr group had the largest mean (15.55 ± 9.17 mm2) among the groups, significant difference only when compared with MC (1.62 ± 0.81 mm2) (p = 0.025). CONCLUSIONS: Translucent monolithic zirconia crowns exhibited significantly higher fatigue and fracture resistance compared with conventional MC and bilayered crowns. CLINICAL SIGNIFICANCE: The appropriate choice of material and manufacturing technique is crucial for predicting the higher clinical performance of single crowns. Enhanced mechanical resistance in terms of fatigue and fracture resistance can be achieved by replacing MC and bilayered restorations with computer-aided design and computer-aided manufacturing monolithic zirconia.

Evaluation of bond strength of glass and resin-ceramics with laser phototherapy: A systematic review and meta-analysis of in vitro studies.

STATEMENT OF PROBLEM: Laser phototherapy has been studied as a surface treatment capable of increasing the adhesion of cement to the ceramic surface. However, the bond strength of glass and resin-ceramics after laser phototherapy is unclear. PURPOSE: The objective of this systematic review and meta-analysis was to compare the bond strength of glass and resin-ceramics using laser therapy and conventional hydrofluoric acid etching. MATERIAL AND METHODS: This systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and was registered in the Open Science Framework (OSF) for in vitro studies. A population, intervention, control, and outcome (PICO) question was formulated: "Does phototherapy promote better bond strength in glass and resin-ceramics than conventional hydrofluoric acid etching?" A literature search was performed in PubMed/MEDLINE, Embase, Web of Science, Scopus, Cochrane Library, and ProQuest databases up to January 2023. The Joanna Briggs Institute critical assessment guidelines for quasi-experimental studies were used for quality assessment. The meta-analysis was based on the inverse variance (IV) method (α=.05). RESULTS: A total of 6 in vitro studies published between 2007 and 2019 with a total number of 348 specimens were included for qualitative analysis; 1 study had a positive effect. Five of the studies were included in the meta-analysis, which indicated a significant decrease for feldspathic ceramics that received laser phototherapy and lithium disilicate (P=.002; MD: -2.15; 95% CI: -3.53 to -0.77; I2=89%, P<.01) and (P<.01; MD: -2.13; 95% CI: -2.99 to -1.27; I2=82%, P<.01), respectively. CONCLUSIONS: Laser irradiation as surface etching of glass ceramics does not produce a bond strength equal to that of conventional hydrofluoric acid etching.

Color stability and surface roughness of resin-ceramics with different surface treatments: A systematic review and meta-analysis of in vitro studies.

STATEMENT OF PROBLEM: Surface treatments for resin-ceramics have been developed to obtain a smooth surface and improve color stability. However, a consensus on the best treatment for these materials is lacking. PURPOSE: The purpose of this systematic review and meta-analysis was to evaluate the color stability and roughness of glass-ceramics versus resin-ceramics with different surface treatments. MATERIAL AND METHODS: The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were followed, and the study was registered in the open science framework (OSF) for in vitro studies. The population, intervention, control, and outcome (PICO) question was "Is there a difference in color stability and roughness between resin-ceramic vs vitreous ceramics in different surface treatment protocols?" A literature search was performed in PubMed/MEDLINE, Embase, Web of Science, Scopus, Cochrane Library, and ProQuest databases up to January 2023. The Joanna Briggs Institute's critical assessment guidelines for quasi-experimental studies were used for quality assessment. The meta-analysis was based on the inverse variance (IV) method (α=.05). RESULTS: A total of 18 laboratory studies were published between 2015 and 2022, with a total of 2160 specimens, all of which were analyzed qualitatively. The meta-analysis indicated significantly less optical alteration for lithium disilicate ceramics (P<.01; MD: 2.69; 95% CI: 2.00-3.39; I²=89%, P<.01), even when compared with resin-ceramics with polish or sealants (P<.01; MD: 2.45; 95% CI: 1.59-3.30; I²=87%, P<.01) and (P<.01; MD: 3.24; 95% CI: 2.02-4.47; I²=89%, P<.01), while there was no significant difference in surface roughness (P=.08; MD: -0.71; CI 95%: -1.52 to 0.09; I²=87%, P<.01) (P=.33; MD: -0.31; CI 95%: -0.94 to 0.32; I²=87%, P<.01), respectively. CONCLUSIONS: Resin-ceramics that have been polished or treated with sealants have lower color stability than glazed glass-ceramics; however, they are similar in terms of surface roughness.

Polyetheretherketone materials for removable partial denture frameworks: an integrative review.

Polyetheretherketone (PEEK) resin is a high-performance thermoplastic polymer that has been introduced as a possible candidate to replace metallic components in dental prostheses. The objective of this integrative review was to compare, through analysis of studies in the literature, the mechanical performance of removable partial denture frameworks and clasps manufactured with PEEK with the performance of cobalt-chromium (Co-Cr) frameworks and clasps. The guiding question was, "Does the use of PEEK as a substitute for Co-Cr alloys for the construction of removable partial denture frameworks result in better mechanical properties?" The PubMed/ MEDLINE, Embase, Web of Science, Scopus, and SciELO databases were searched for articles published through October 2021. The JBI Critical Appraisal Checklist for Quasi-Experimental Studies was used to assess the methodologic quality of the selected in vitro studies. A total of 208 articles were identified. After the exclusion of duplicates and articles that did not meet the inclusion criteria, 7 studies- -4 in vitro and 3 three-dimensional finite element analyses- -published between 2012 and 2021 were included in the integrative review. The appraisal checklist revealed that the reviewed studies had a low risk of bias and high methodologic quality. The results of the review showed that PEEK alloys have adequate mechanical properties for use in clasps and removable partial denture frameworks, but Co-Cr alloys exhibit better mechanical properties and are more suitable in most circumstances.

Survival and complications of monolithic ceramic for tooth-supported fixed dental prostheses: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Although recent studies have reported the success of implant-supported monolithic restorations, consensus on the use of monolithic ceramic restorations is lacking. PURPOSE: The purpose of this systematic review and meta-analysis was to evaluate the survival and biological and technical complication rates of monolithic single crowns and fixed partial dentures (FPDs). MATERIAL AND METHODS: An electronic search was conducted by 2 independent authors on the PubMed/MEDLINE, Scopus, and Cochrane Library databases. The Newcastle-Ottawa scale and Cochrane risk of bias tool were used to assess the quality and risk of bias of the included studies. Meta-analysis was performed by using the R software program. RESULTS: The search identified 763 articles, 18 of which met the eligibility criteria. A total of 15 studies evaluated monolithic ceramic single crowns, and 4 studies evaluated FPDs. The studies included 1061 monolithic single crowns (524 lithium disilicate, 461 zirconia, and 76 polymer-infiltrated ceramic network [PICN]) and 104 FPDs (36 lithium disilicate and 68 zirconia). Meta-analysis of single-arm studies indicated the proportion of survival, biological, and technical complication rates of 1% (95% confidence interval [CI]: 0% to 3%), 1% (CI: 0% to 4%), and 2% (CI: 1% to 4%), respectively, for single crowns, independent of ceramic material, and 3% (CI: 0% to 34%), 5% (CI: 1% to 21%), and 5% (CI: 1% to 21%) for FPDs, respectively. Only 5 studies performed a direct comparison between monolithic and veneered ceramic restorations, and no significant difference was observed in terms of survival (risk ratio [RR]: 0.68; CI: 0.25-1.91; P=.96), biological (RR: 0.69; CI: 0.31-1.53; P=.35), and technical complication rates (RR: 0.87; CI: 0.40-1.88; P=.29). CONCLUSIONS: The use of monolithic ceramic can be considered a favorable treatment for tooth-supported single crowns and FPDs, with high survival and low complication rates. However, further randomized controlled trials are needed to reassess these clinical performances, mainly by comparing them with the performance of veneered restorations.

Effect of handling material on mechanical and optical properties of feldspathic porcelain.

OBJECTIVE: To evaluate the optical, chemical, and mechanical properties of feldspathic porcelain after handling with different instrument materials. MATERIAL AND METHODS: Feldspathic porcelain was manipulated with different spatula compositions: metal spatula (MS), plastic spatula (PS), and glass spatula (GS) for the fabrication of 30 (n = 10) disks. Contrast ratio (CR), translucency parameter (TP), and surface Knoop microhardness (KHN) were measured. The color change (ΔE00 ) was evaluated using the CIEDE2000 system. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used for surface analysis. Data were analyzed using one-way ANOVA and Tukey test (P < 0.05). RESULTS: All groups presented different morphological surfaces with higher presence of Al on the MS. PS group presented lower Al, Si, K than MS, and GS. Higher CR was observed for PS (0.734; P < 0.043), followed by MS (0.696; P < 0.043) and GS (0.65; P < 0.011). The highest TP (13.06) and KHN (386.27) were presented by GS (P < 0.001). MS and PS presented similar KHN results. The higher ΔE00 were found for plastic/metal comparison. Also, the L* values for the MS group (67.49) were lower than the other groups. CONCLUSION: The use of metal spatula promoted higher color alteration during feldspathic porcelain manipulation than did the other materials. Handling with glass instrument promoted higher microhardness than other spatula materials. CLINICAL SIGNIFICANCE: The effect of the material used for ceramic handling on feldspathic porcelain properties is often ignored. This study shows that the handling spatula material must be carefully chosen to avoid inadvertent changes to the feldspathic porcelain restoration.

The Effect of Surface Treatment on Shear Bond Strength between Y-TZP and Veneer Ceramic: A Systematic Review and Meta-Analysis.

PURPOSE: The objective of this systematic review with meta-analysis was to evaluate surface treatment in yttria-stabilized tetragonal zirconia polycrystal ceramic (Y-TZP) on the shear bond strength (SBS) values between Y-TZP (core ceramic) and veneer ceramic, compared to untreated specimens. MATERIALS AND METHODS: This review was registered at PROSPERO platform under the number CRD42016036493. The systematic review of the extracted publications was performed to compare the effect of surface treatment on SBS between Y-TZP ceramic and veneering ceramic. A comprehensive review of the literature from the earliest available dates through January 2017 was performed in the PubMed/Medline, Embase, Scopus, and Cochrane Library databases. RESULTS: A total of 15 studies were identified for the inclusion of data, with only in vitro studies. A random-effect model found statistically significant differences between untreated and treated surfaces of Y-TZP (p < 0.00001; MD: 2.84; 95% CI: 2.19 to 3.49). In another analysis, a random-effect model found statistically significant differences between the groups that only performed the associations of treatments and control group (p < 0.00001; MD: 3.19; 95% CI: 2.11 to 4.28). CONCLUSIONS: Surface treatment in Y-TZP improved the values of SBS between the Y-TZP and veneer ceramic. The associations between two or more treatments also showed positive effect on the bond strength due the cumulative effect of the treatments.

Stress Distribution in an Implant-Supported Mandibular Complete Denture Using Different Cantilever Lengths and Occlusal Coating Materials.

PURPOSE: The aim of this study was to assess stress distribution in the bone-implant interface of a mandibular implant-supported prosthesis with different cantilever lengths, aesthetic coating materials, and implant abutments. MATERIALS AND METHODS: A photoelastic model of an edentulous mandible, containing 5 external hexagon implants, was constructed. Experimental models were divided into 6 groups: group 1-UCLA component and metal bar; group 2-UCLA component and acrylic resin coating; group 3-UCLA component and porcelain coating; group 4-abutment and metal bar; group 5-abutment and acrylic resin coating; and group 6-abutment and porcelain coating. Forces were applied to the most anterior implant, the most posterior implant, and different cantilever lengths. RESULTS: The results showed a higher number of high-stress fringes as the cantilever length increased. Fringes were better distributed in groups with prostheses composed of acrylic resin and in groups that contained an abutment. CONCLUSION: The stress distribution in the bone-implant interface is improved when the cantilever is eliminated and when abutments in an acrylic resin prosthesis are used.

A photoelastic and strain gauge comparison of two attachments for obturator prostheses.

STATEMENT OF PROBLEM: The rehabilitation of patients after a maxillectomy involves the use of an obturator to seal oral-nasal-sinus communication and to facilitate mastication, swallowing, and speech. PURPOSE: The purpose of this in vitro study was to evaluate different attachment systems used for implant-retained obturators at dissipation loads and under shear forces. MATERIAL AND METHODS: Photoelastic models were fabricated with 3 external hexagon implants at the incisor, canine, and first molar regions. Subsequently, overdentures were made, and metal hooks were placed at the incisor and first molar regions to displace the prostheses in the vertical, anterior, and posterior directions, with a constant speed of 50 mm/min. A photoelastic model with an O-ring or bar-clip system was placed in a circular polariscope, and tested with a universal testing machine. The images were recorded and high-intensity fringes were counted using software. For strain gauge analysis, each strain gauge was placed horizontally at the mesial and distal sides of the implants. The registered strains were submitted to 2-way ANOVA (α=.05). RESULTS: The O-ring showed the lowest number of high-intensity fringes in photoelastic imaging, while the strain gauge analysis showed the lowest stress values in the bar-clip group (P=.007). CONCLUSIONS: The stress around titanium implant necks was more damaging to surrounding bone, while the bar-clip attachment system had a better biomechanical performance. The bar-clip presented the lowest strain values around the dental implants and few high-intensity fringes.

The Effect of Disinfection Techniques on the Flexural Strength of Thermopolymerisable Acrylic Resins With or Without Pigment Addition.

OBJECTIVES: The aim of this study was to assess the flexural strength of two brands of thermopolymerisable acrylic resins (Onda Cryl, Artigos Odontológicos Clássico Ltda, São Paulo, SP, Brazil; and Lucitone 550, Dentsply, York, PA, USA) with varying concentrations of pigment (Poli-Côr, Artigos Odontológicos Clássico Ltda, São Paulo, SP, Brazil) under the influence of thermocycling, storage and disinfection. MATERIAL AND METHODS: A total of 210 samples were manufactured (105 for each acrylic resin brand), with dimensions of 64 x 10 x 3.3 mm. The samples were divided into 30 subgroups (n = 7) according to the proportion of pigment used (without pigment, 3% and 7%), the assessment period (initial or thermocycling for 2000 cycles) and disinfection method (immersion in 1% sodium hypochlorite, (Apothicário, Araçatuba, SP, Brazil), microwave energy or immersion in alkaline peroxide (Efferdent, Pfizer, Morris Plains, NJ, USA). The samples were submitted to the flexural strength test before and after thermocycling, and after storage with disinfection. The disinfection process was performed every 3 days, for 60 days. Data were submitted to analysis of variance (ANOVA) and Tukey test (p < 0.05). RESULTS: The factors that provided statistical alteration in flexural strength values were resin type and assessment period. The Onda Cryl resin and the period after disinfection (126 ± 25 MPa) exhibited the higher values of flexural strength. CONCLUSION: Following disinfection, Onda-Cryl resin exhibited the highest values of flexural strength. All the samples obtained are considered clinically acceptable.

Use of stress analysis methods to evaluate the biomechanics of oral rehabilitation with implants.

Because the biomechanical behavior of dental implants is different from that of natural tooth, clinical problems may occur. The mechanism of stress distribution and load transfer to the implant/bone interface is a critical issue affecting the success rate of implants. Therefore, the aim of this study was to conduct a brief literature review of the available stress analysis methods to study implant-supported prosthesis loading and to discuss their contributions in the biomechanical evaluation of oral rehabilitation with implants. Several studies have used experimental, analytical, and computational models by means of finite element models (FEM), photoelasticity, strain gauges and associations of these methods to evaluate the biomechanical behavior of dental implants. The FEM has been used to evaluate new components, configurations, materials, and shapes of implants. The greatest advantage of the photoelastic method is the ability to visualize the stresses in complex structures, such as oral structures, and to observe the stress patterns in the whole model, allowing the researcher to localize and quantify the stress magnitude. Strain gauges can be used to assess in vivo and in vitro stress in prostheses, implants, and teeth. Some authors use the strain gauge technique with photoelasticity or FEM techniques. These methodologies can be widely applied in dentistry, mainly in the research field. Therefore, they can guide further research and clinical studies by predicting some disadvantages and streamlining clinical time.

Fabrication techniques for ocular prostheses--an overview.

The goals of treatment with ocular prostheses are to restore facial aesthetics and self-esteem to anophthalmic patients. Fabricated in acrylic resin, artificial eyes should be aesthetically pleasing, scratch-resistant, and adequately polished. Use of a prosthesis without such characteristics can lead to psychological damage, as well as infection and inflammation due to the accumulation of microorganisms and other substances on an irregularly shaped prosthesis. The present literature review describes the different techniques for fabricating ocular prostheses. Reproduction of the iris color and color stability are important factors that promote adequate aesthetics. The fabrication of an individual ocular prosthesis in acrylic resin provides satisfactory aesthetic results because the impression process establishes the defect contour. Additionally, the iris and sclera can be individually characterized. As the techniques, materials, and manufacturing methods for ocular prostheses continue to evolve, the aesthetics and functionality of prostheses will also improve.

Effect of beverages and mouthwashes on the hardness of polymers used in intraoral prostheses.

PURPOSE: The mechanical properties of acrylic resins used in intraoral prostheses may be altered by frequent exposure to liquids such as beverages and mouthwashes. This study aimed to evaluate the effect of thermocycling and liquid immersion on the hardness of four brands of acrylic resins commonly used in removable prostheses (Onda Cryl, QC-20, Clássico, Lucitone). MATERIALS AND METHODS: For each brand of resin, seven specimens were immersed in each of six solutions (coffee, cola, red wine, Plax-Colgate, Listerine [LI], Oral B), and seven more were placed in artificial saliva (control). The hardness was tested using a microhardness tester before and after 5000 thermocycles and after 1, 3, 24, 48, and 96 hours of immersion. The results were analyzed using three-way repeated-measures ANOVA and Tukey's test (p < 0.05). RESULTS: The hardness of the resins decreased following thermocycling and immersion in the solutions. Specimens immersed in cola and wine exhibited significant decreases in hardness after immersion for 96 hours, although the greatest significant decrease in hardness occurred in specimens immersed in LI. However, according to American Dental Association specification 12, the Knoop hardness of acrylic resins for intraoral prostheses should not be below 15. Thus, the median values of superficial hardness observed in most of the acrylic resins in this study are considered clinically acceptable. CONCLUSIONS: The microhardness of polymers used for intraoral prostheses decreases following thermocycling. Among specimens immersed in beverages, those immersed in cola or wine experienced the greatest decrease in microhardness. Immersion of acrylic resins in LI significantly decreased the microhardness in relation to the initial value. Among the resins assessed, QC-20 exhibited the lowest initial hardness.

Comparison of self-etching and conventional bifunctional coupling agent in lithium disilicate ceramic: A systematic review and meta-analysis.

Background: The aim of this systematic review is to determine the effectiveness of self-etching primers in comparison to the conventional protocol with hydrofluoric acid and silane treatment for bonding lithium disilicate ceramics. Material and Methods: The formulated PICO question for this research was: "Does self-etching silane primer surface treatment in lithium disilicate ceramics present a similar bond strength value compared to conventional hydrofluoric acid and silane treatment?". Combinations of words and appropriate truncations were adapted for each database. For the selection, duplicate articles were systematically eliminated using Mendeley software. The Cohen's Kappa statistic was then computed, RoBDEMAT questions were addressed, and the meta-analyses were conducted using RevMan 5.4, at a significance level of 5%. Results: Two independent reviewers conducted a blind and independent analysis of 190219 articles from PubMed, Scopus, Web of Science, and OpenGrey. Subsequently, they extracted data from 21 studies for the systematic review and in 16 the meta-analysis. In all in vitro studies, the most frequently cited concentration of hydrofluoric acid was 5%. In the meta-analysis, no statistical differences were observed between the two treatments concerning bond strength. Conclusions: Self-etching silane primers demonstrate promising results in lithium disilicate bonding, suggesting their potential as an alternative surface treatment to hydrofluoric acids + silane. Key words:Lithium disilicate, Hydrofluoric acid, Dental Porcelain, Ceramics, Silanes.

Stress distribution in implant-supported prosthesis with external and internal implant-abutment connections.

OBJECTIVE: This study aimed to investigate the stress distribution in screwed implant-supported prostheses with different implant-abutment connections by using a photoelastic analysis. MATERIALS AND METHODS: Four photoelastic models were fabricated in PL-2 resin and divided according to the implant-abutment connection (external hexagon (EH) and Morse taper (MT) implants (3.75 × 11.5 mm)) and the number crowns (single and 3-unit piece). Models were positioned in a circular polariscope and 100-N axial and oblique (45) loading were applied in the occlusal surface of the crowns by using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using software (Adobe Photoshop). RESULTS: Under axial loading, the MT implants exhibited a lower number of fringes for single-unit crowns than EH implants, whereas for a 3-unit piece the MT implants showed a higher number of fringes vs EH implants. The oblique loading increased the number of fringes for all groups. CONCLUSION: In conclusion, the MT implant-abutment connection reduced the amount of stress in single-unit crowns, for 3-unit piece crowns the amount of stress was lower using an external hexagon connection. The stress pattern was similar for all groups. Oblique loading promoted a higher stress concentration than axial loading.

Evaluation of the mechanical properties of different materials for manufacturing occlusal splints.

This study aimed to compare the mechanical properties of various occlusal plate materials by analyzing surface roughness, Knoop microhardness, flexural strength, and modulus of elasticity. Fifty samples were prepared and classified as SC (self-curing acrylic resin), WB (heat-cured acrylic resin), ME (acrylic resin polymerized by microwave energy), P (resin print), and M (polymethylmethacrylate polymer block for computer-aided design/computer-aided manufacturing). The data were analyzed using a one-way analysis of variance and Tukey's honestly significant difference test. Surface roughness was the same in all groups. The surface hardness of group M was statistically superior. The samples from groups P and M had higher flexural strength than other samples. The modulus of elasticity of group SC was statistically lower than that of other groups. The mechanical properties of the materials used to make the occlusal plates differed, and group M achieved the best results in all analyses. Therefore, clinicians must consider the material used to manufacture long-lasting and efficient occlusal splints.

Use of facial protection to prevent reinjury during sports practice.

The objective of the study was to report the prevention of facial reinjury of a volleyball player using a custom-made protective facial shield. A custom-made protective partial facial shield was fabricated using polymethylmethacrylate and was fitted with a soft lining material to provide additional comfort and protection to the injured area. Facial protection provides greater security against possible facial injuries and allows injured areas to recover during sports practice.

Effect of thermocycling on hardness, absorption, solubility and colour change of soft liners.

OBJECTIVE: The effect of artificial ageing on the hardness, absorption, solubility, and colour of soft denture liners was investigated. MATERIALS AND METHODS: Liner materials based on acrylic resin (Trusoft) or silicone (Dentusil, Ufi Gel P, and Ufi Gel SC) were tested before and after 2000 thermal cycles. A total of 20 specimens of each material were tested. Half of the specimens were used for hardness and colour evaluation, and the remainder for absorption and solubility tests. The hardness evaluation was carried out using a Shore A durometer, while absorption and solubility tests were performed by storing samples in a desiccator and weighing daily until reaching constant mass (W1). After thermocycling, the samples were again weighed (W2) and dried (W3). Colour was measured using a spectrophotometer. Statistical analysis was performed using GraphPad InStat at the p < 0.05 level. RESULTS: Thermocycling significantly affected the hardness of the specimens. The Trusoft material exhibited the highest absorption (1.48 ± 0.48), solubility (1.26 ± 0.28), and colour change (3.92 ± 0.33), significantly different from the other materials. There were no significant differences among the silicones in terms of absorption, solubility, and colour change, except for the colour of Dentusil, which changed (0.83 ± 0.11). CONCLUSION: It can be concluded that silicone liners performed significantly better compared to acrylic resin.

Silica deposition on zirconia via room-temperature atomic layer deposition (RT-ALD): Effect on bond strength to veneering ceramic.

PURPOSE: To develop and to characterize a hybrid interface between yttria-stabilized zirconia (Y-TZP) transformed layer and silica-based nanofilm to enable a better bonding between Y-TZP and a veneering ceramic. MATERIAL AND METHODS: Sixty-six fully-sintered rectangular Y-TZP specimens were distributed into 6 groups, according to the surface treatment applied: C (control): no treatment; Al: 27 µm-alumina particle abrasion; Ht: hydrothermal treatment in autoclave for 15h; Si20: 20 cycles of silica deposition using room-temperature atomic layer deposition (RT-ALD); Si40: 40 cycles of RT-ALD; Ht + Si40: hydrothermal treatment followed by 40 cycles of RT-ALD. RT-ALD was performed by the sequential exposure of specimens to vapor of tetramethoxysilane orthosilicate (TMOS) and ammonium hydroxide (NH4OH). Y-TZP surface wettability and shear bond strength (SBS) between Y-TZP and the veneering ceramic were analyzed for all groups after surface treatments. One-way ANOVA and Tukey's HSD test were used for data analysis (p ≤ 0.05). RESULTS: The highest contact angle was observed for the control group (64.46 ± 6.09 θ), while the lowest values (p < 0.001) were presented after Si20 (29.85 ± 4.23 θ) and Si40 (30.37 ± 5.51 θ) treatments. Hydrothermal treatment (49.3 ± 2.69 θ) and alumina abrasion (45.84 ± 4.12 θ) resulted in intermediate contact angle values. The highest SBS values were observed for Al (16.74 ± 1.68 MPa) and Ht (15.27 ± 2.11 MPa) groups (p < 0.018). Groups Si20 (9.66 ± 1.22 MPa), Si40 (9.33 ± 2.11 MPa), Ht + Si40 (9.37 ± 1.02 MPa) and C (12.54 ± 2.64 MPa) all resulted in similar SBS results (p > 0.998). CONCLUSION: The experimental treatments proposed enhanced surface wettability, but shear bond strength between Y-TZP and veneering ceramic was not improved. Alumina particle-abrasion improved SBS values while a decrease in wettability was observed.

Stress distribution of multiple implant-supported prostheses: Photoelastic and strain gauge analyses of external hexagon and morse taper connections.

Background: To evaluate the stress distribution of three-element prostheses on two different implant systems (External Hexagon (EH) or Morse Taper (MT)) and with two different retention mechanisms (screw-retained or cemented), by photoelastic analysis and strain gauge analyses. Material and Methods: Four photoelastic and 24 strain gauge models of a partially edentulous maxilla were made and were divided in four groups according to connection and retention system: Group I (EH-C) - external hexagon+cement-retained prosthesis; Group II (EH-S) external hexagon+screw-retained prosthesis; Group III (MT-C) - morse taper+cement-retained prosthesis; Group IV (MT-S) - morse taper+screw-retained prosthesis. The implants were installed in the axial position, the first in the region of element 15 and the distal implant in the region of element 17. Loads of 100 N were applied on the occlusal surface of the prosthesis for 10 seconds. For the photoelasticity analysis, photographic images were taken and were evaluated according to the number of high-intensity fringes. For the strain gauge analysis, the strain gauges were positioned on the marginal crest of the implants and on the apical region, being numbered for analysis of the stress distribution in each region. The electrical signals were captured and processed by specific software. Results: Higher concentration of tension was observed in the apical region of the implants and mainly in the distal implant, where the formation of fringes was higher. The microstrain values obtained for each group were similar: EH-C (454±18,3 µÉ›); EH-S (469±94 µÉ›); MT-C (466±49,8 µÉ›); MT-S (460±36,6 µÉ›). It was observed that apical position had higher stress concentrations for all analyzed groups. Conclusions: The different connections and fixation mode did not interfere in the amount of tension generated in the tissue adjacent to the implant, also the region that generated the greatest amount of tension was in the apical region of the anterior implant. Key words:Dental implants, biomechanics, fixed prosthodontics.